random: Fix test compilation failure on Cygwin 1.5.25. * m4/stdlib_h.m4 (gl_STDLIB_H_DEFAULTS): Initialize HAVE_DECL_INITSTATE, HAVE_DECL_SETSTATE. * m4/random.m4 (gl_FUNC_RANDOM): Test whether initstate and setstate are declared. * modules/stdlib (Makefile.am): Substitute HAVE_DECL_INITSTATE, HAVE_DECL_SETSTATE. * lib/stdlib.in.h (initstate): Declare also if HAVE_DECL_INITSTATE is 0. (setstate): Declare also if HAVE_DECL_SETSTATE is 0. * doc/posix-functions/initstate.texi: Mention the Cygwin 1.5.x problem. * doc/posix-functions/random.texi: Likewise. * doc/posix-functions/setstate.texi: Likewise. * doc/posix-functions/srandom.texi: Likewise.